Optimizing retention time and peak width reproducibility with high peak capacity in high-speed gas chromatography...

We are developing high speed gas chromatographic (HSGC) instrumentation with an optimizable injection system, referred to herein as dynamic pressure gradient injection (DPGI). In the present study, we examine the effects of the DPGI pulse width and linear flow velocity on the resultant chromatographic peak widths and separation peak capacity. DPGI readily yields reproducible peak widths and retention times in a sub-second separation runtime regime over long periods of repeated injections. These repeated measurements facilitate a statistically rigorous analysis of the relationships between peak widths obtained and injection pulse width and/or linear flow velocity. Chromatographic performance was studied using a 1 m × 100 µm × 0.1 µm Rtx-5 chromatographic column at various linear flow velocities with hydrogen as the carrier gas, an isothermal temperature of 100 °C, with a test mixture of acetone, nonane, decane and undecane. At this column temperature, acetone is nominally unretained. For conditions where plate height is minimized (H_min) at the so-called optimum linear flow velocity, u_opt, and with the off-column band broadening approaching zero by optimizing DPGI performance, an H_min of 77 µm was obtained. The chromatographic data corresponding to this H_min included a minimum peak width-at-half height (w_1/2) of 8±0.2ms for acetone, and a peak capacity (n_c)of ∼30 for a separation runtime of 1.2 s. When all that is needed is the separation of a few key analytes as fast as possible, and if some peak capacity can be sacrificed, the fastest separation studied yielded a minimum peak width at half-height w_1/2=5.5±0.09ms for acetone, and a n_c of 10 with a separation runtime of 325ms.